1. Field of the Invention
This invention relates generally to voltage/power converters, and more particularly, to an improved DC-to-DC converter input stage.
2. Description of the Related Art
A DC-to-DC converter is an electronic circuit, which converts a source of direct current (DC) from one voltage level to another, and is considered a class of power converter. Most DC-to-DC converters also regulate the output voltage. There are various different types of DC-to-DC converters/regulators, including linear regulators, electronic switch-mode converters, magnetic converters, and switched capacitor converters, among others. Linear regulators are used to downconvert higher input voltages to lower output voltages. Magnetic DC-to-DC converters periodically store and release energy in and from a magnetic field in an inductor or a transformer. Electronic switch-mode DC-to-DC converters convert one DC voltage level to another by temporarily storing the input energy, then releasing the stored energy to the output at a different voltage level. Switched capacitor converters operate by alternately connecting different capacitor topologies between the input and output. Voltage conversion is also performed by switching voltage regulators, which incorporate a switching mechanism to efficiently convert electrical power. Unlike linear power supplies, the pass transistor of switching voltage supplies continually switches between low-dissipation, full-on and full-off states, residing in a high dissipation state for only very brief periods of time, thereby minimizing energy loss. Switching voltage regulators often use two or more power transistors to convert energy at one voltage to another voltage.
In DC-to-DC converters, it is typically necessary to limit the amount of power provided in order to avoid surges during startup, and/or avoid damaging any circuit component during a fault condition. In some applications, the output of a power converter may be expected to supply brief, large surges of power, and it may be desirable to draw this power from the energy stored in the output capacitor rather than from the input power supply that provides the input voltage to the converter. This may also be achieved by limiting the amount of power delivered by the input. There are a number of existing solutions to this problem, each with its own drawbacks.
The current drawn from the input can be measured, and the converter can actively respond to regulate this current down to a certain maximum value. This typically requires an active control loop, which adds considerable design complexity, and has to be stabilized during normal operation. The current measurement is typically performed through the use of a series resistor, which can waste power even when the current limit is not reached. A series output resistance can be simulated with a series reactance that has an impedance related to the switching frequency of the converter. This limits the power provided by the converter without unduly hurting efficiency, but prevents the output from approximating a constant voltage source even when the power limit is not reached, and an approximately constant voltage output is an extremely desirable, common characteristic of DC-to-DC converters.
The direct draw of brief power surges from the input power supply can be prevented, by using sufficient filtering. Persistent fault conditions can be detected, and the converter can shut down in response. In addition, startup surges can be reduced, by altering the converter's behavior only during startup. However, the necessary filtering tends to require large inductors that are unacceptable in space-constrained applications. Shutting down the converter during a fault condition requires an explicit fault detection and reset mechanism. Similarly, a distinct start-up behavior requires the ability to detect that the converter is in a start-up condition, and respond appropriately, all of which add a considerable amount of design complexity.
Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.